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United States Patent |
6,213,692
|
Guehring
,   et al.
|
April 10, 2001
|
Cutting tool
Abstract
A cutting tool, especially a drill, milling cutter, screw tap, reamer and
core drill, comprising a shaft and a cutting member on which at least one
cutting edge is provided for machining a workpiece, the cutting member
being provided with a slide layer which has a lower hardness than a base
layer of the cutting member.
Inventors:
|
Guehring; Joerg (Fran-Schubert-Strasse 18, 72458 Albstadt, DE);
Cselle; Tibor (Sigmaringen, DE);
Rechberger; Johann (Bern, CH)
|
Assignee:
|
Vilab AG (Bern, CH);
Guehring; Joerg (Albstadt, DE)
|
Appl. No.:
|
930246 |
Filed:
|
December 4, 1997 |
PCT Filed:
|
March 28, 1996
|
PCT NO:
|
PCT/EP96/01374
|
371 Date:
|
December 4, 1997
|
102(e) Date:
|
December 4, 1997
|
PCT PUB.NO.:
|
WO96/30148 |
PCT PUB. Date:
|
October 3, 1996 |
Foreign Application Priority Data
| Mar 30, 1995[DE] | 195 11 828 |
| Mar 30, 1995[DE] | 195 11 829 |
| Jan 31, 1996[DE] | 296 01 653 U |
Current U.S. Class: |
408/144; 408/223; 408/230 |
Intern'l Class: |
B23B 051/02 |
Field of Search: |
408/144,223,224,227,229,230,145
407/53
|
References Cited
U.S. Patent Documents
3945807 | Mar., 1976 | Fukutome | 408/144.
|
4802799 | Feb., 1989 | Rachev.
| |
4826365 | May., 1989 | White.
| |
5011342 | Apr., 1991 | Hsu.
| |
5160232 | Nov., 1992 | Maier.
| |
5312209 | May., 1994 | Lindblom | 408/230.
|
5452971 | Sep., 1995 | Nevills | 408/230.
|
5509761 | Apr., 1996 | Grossman et al. | 408/230.
|
Foreign Patent Documents |
84413 | Mar., 1895 | DE.
| |
1 017 438 | Oct., 1957 | DE.
| |
1 296 805 | Jun., 1969 | DE.
| |
2 021 688 | Aug., 1972 | DE.
| |
2 357 134 | Nov., 1973 | DE.
| |
2 240 646 | Nov., 1974 | DE.
| |
25 05 555 | Aug., 1975 | DE.
| |
202 898 | Oct., 1983 | DE.
| |
31 31 794 | Aug., 1986 | DE.
| |
36 28 262 | Jan., 1988 | DE.
| |
37 04 106 | Aug., 1988 | DE.
| |
37 30 378 | Mar., 1989 | DE.
| |
37 30 377 | Mar., 1989 | DE.
| |
38 26 239 | Feb., 1990 | DE.
| |
99549 | Mar., 1997 | DE.
| |
99 549 | Mar., 1997 | DE.
| |
714611 | Nov., 1931 | FR | 408/224.
|
2650299 | Feb., 1991 | FR | 408/144.
|
660 129 | Oct., 1951 | GB.
| |
2 201 910 | Sep., 1988 | GB.
| |
48413 | Mar., 1987 | JP | 408/144.
|
216706 | Aug., 1989 | JP | 408/144.
|
1060344 | Dec., 1983 | SU | 408/230.
|
1812003 | Apr., 1993 | SU | 408/230.
|
WO 89/02328 | Mar., 1989 | WO.
| |
Other References
"Machining Tools for Special Purpose Machine Engineering and Automatic
Production Cycle Lines", pp. 67 and 68, 1972.
|
Primary Examiner: Howell; Daniel W.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
Claims
What is claimed is:
1. A cutting tool, comprising:
a cutting member including,
a base body defining at least one open face and at least one flute
intersecting to form at least one cutting edge configured to splinter
material off a workpiece,
said open face and said flute including plural adjacent groove-shaped
recesses; forming a continuous undulating cross section at said cutting
edge, and
a slide layer formed on at least a portion of said base body and having a
lower hardness than said base body.
2. A cutting tool according to claim 1, wherein said slide layer comprises
a sulfide, a selenide, a telluride, or a mixed combination thereof.
3. A cutting tool according to claim 2, wherein said slide layer includes a
material selected from the group consisting of MoS.sub.2, NbS.sub.2,
TaS.sub.2, WS.sub.2, MoSe2, NbSe.sub.2, TaSe.sub.2, Wse.sub.2, MoTe2,
NbTe.sub.2, Wte.sub.2, and mixed compounds thereof.
4. A cutting tool according to claim 1, wherein said base body of said
cutting member comprises a material selected from the group consisting of
high speed steel (HSS), a hard alloy, cermit and ceramic.
5. A cutting tool according to claim 1, wherein said slide layer is not
provided in the area of said cutting edge.
6. A cutting tool according to claim 1, wherein a thickness of said slide
layer is between 0.01-5 .mu.m.
7. A cutting tool according to claim 1, wherein the hardness of said slide
layer is between 1-2 on the Mohs' hardness scale.
8. A cutting tool according to claim 1, wherein said plurality of adjacent
groove shaped recesses of said open face extend away from said cutting
edge toward a rear edge of said open face.
9. A cutting tool according to claim 6, wherein said cutting edge is formed
on a front edge of said open face and said groove shaped recesses of said
open face are arranged in an approximately concentric relationship
relative to a lengthwise axis of said cutting tool.
10. A cutting tool according to claim 7, wherein said groove shaped
recesses of said open face are segments of a circle or spiral.
11. A cutting tool according to claim 1, wherein said groove shaped
recesses of said flute are formed such that an axis of said groove shaped
recesses of said flute run approximately parallel to an axis of said
flute.
12. A cutting tool according to claim 9, wherein said groove shaped
recesses of said open face form an approximately undulatory cross section.
13. A cutting tool according to claim 9, wherein one of said plurality of
groove shaped recesses of said open face is allocated to one of said
plurality of groove shaped recesses of said flute, respectively, with said
one groove shaped recess of said open face forming an extension of said
one groove shaped recess of said flute.
14. A cutting tool according to claim 1, wherein said groove shaped
recesses of said open face and said groove said recess of said flute
extend away from said cutting edge and run across only a partial section
of at-least one of said flute and said open face.
15. A cutting tool according to claim 1, wherein the width and depth of
said groove shaped recesses of at least one of said open face and said
flute is 0.01-2 mm.
16. A cutting tool according to claim 1, wherein the width and depth of
said groove shaped recesses of at least one of said open face and said
flute is 0.02-0.5 mm.
17. A cutting tool, comprising:
a cutting member, including
a base body defining at least one open face and at least one flute
intersecting at least one cutting edge configured to splinter material off
a workpiece,
said open face and said flute including plural adjacent groove-shaped
recesses forming a continuous undulating cross section at said cutting
edge,
a base layer formed on at least a portion of said base body, and
a slide layer formed on at least on at least a portion of at least one of
said base layer and said base body, said slide layer having a lower
hardness than said base layer and said base body.
18. A cutting tool according to claim 17, wherein said slide layer
comprises a sulfide, a selenide, a telluride, or a mixed combination
thereof.
19. A cutting tool according to claim 18, wherein said slide coating layer
includes a material selected from the group consisting of MoS.sub.2,
NbS.sub.2, TaS.sub.2, WS.sub.2, MoSe.sub.2, NbSe.sub.2, TaSe2, Wse.sub.2,
MoTe.sub.2, NbTe.sub.2, Wte.sub.2, and mixed compounds thereof.
20. A cutting tool according to claim 17, wherein said base body of said
cutting member comprises a material selected from the group consisting of
high speed steel (HSS), a hard alloy, cermit and ceramic.
21. A cutting tool according to claim 17, wherein said base layer comprises
a ceramic material.
22. A cutting tool according to claim 21, wherein said base layer includes
a material selected from the group consisting of TiN, TiAlN, TiCN, and
diamond.
23. A cutting tool according to claim 17, wherein said slide layer is not
provided in the area of said cutting edge.
24. A cutting tool according to claim 17, wherein a thickness of said base
layer is between 1-10 .mu.m.
25. A cutting tool according to claim 17, wherein a thickness of said slide
layer is between 0.01-5 .mu.m.
26. A cutting tool according to claim 17, wherein a thickness of said base
layer is between 1-10 .mu.m and a thickness of said slide layer is between
0.01-5 .mu.m.
27. A cutting tool according to claim 17, wherein the hardness of said base
layer is between 1,000 and 10,000 HV and the hardness of said slide layer
is between 1-2 on the Mohs' hardness scale.
28. A cutting tool according to claim 17, wherein the hardness of said base
layer is between 2,000 and 4,000 HV and the hardness of said sliding layer
is between 1-2 on the Mohs' hardness scale.
29. A cutting tool according to claim 17, wherein a plurality of adjacent
groove shaped recesses of said open face extend away from said cutting
edge toward a rear edge of said open face.
30. A cutting tool according to claim 26, wherein said cutting edge is
formed on a front edge of said open face and said groove shaped recesses
of said open face are arranged in an approximately concentric relationship
relative to an axis of said cutting tool.
31. A cutting tool according to claim 27, wherein said groove shaped
recesses of said open face are segments of a circle or spiral.
32. A cutting tool according to claim 17, wherein said groove shaped
recesses of said flute are formed such that an axis of said groove shaped
recesses run approximately parallel to an axis of said flute.
33. A cutting tool according to claim 30, wherein said groove shaped
recesses of at least one of said open face and said flute form an
approximately undulatory cross section.
34. A cutting tool according to claim 30, wherein one of said plurality of
groove shaped recesses of said open face is allocated to one of said
plurality of groove shaped recesses of said flute, respectively, with said
one groove shaped recess of said open face forming an extension of said
one groove shaped recess of said flute.
35. A cutting tool according to claim 17, wherein said groove shaped
recesses of said open face and said groove shaped recess of said flute
extend away from said cutting edge and run across only a partial section
of at least one of said open face and said flute.
36. A cutting tool according to claim 17, wherein the width and depth of
said groove shaped recesses of at least one of said open face and said
flute is 0.01-2 mm.
37. A cutting tool according to claim 17, wherein the width and depth of
said groove shaped recesses of at least one of said open face and said
flute is 0.02-0.5 mm.
Description
The invention relates to a cutting tool such as a drill, milling cutter,
screw tap, reamer or core drill in accordance with the preamble of claim
1.
The use of numerically controlled machine tools has been a substantial
contribution to increasing the productivity, flexibility, manufacturing
quality and efficiency of modern production apparatuses. The versatile
possibilities of control technique and information processing have been
responsible for machine designs suited for use in automatic manufacturing
systems. Systems of this kind are usually equipped with tool and workpiece
storage means, automatic changing means and integrated measuring stations
so that the steps to be manually taken by the machine operator are
minimized. Sensors for monitoring machine functions and process states,
such as wear and breakage of tools, ensure the automatic manufacturing
sequence. In order to be able to exploit the full capacity of such machine
tools, in parallel with the development of machine tools also appropriate
tools have to be provided which permit a prolonged tool life as well as an
increase in the cutting speeds so that the manufacturing times can be
reduced to a minimum. However, in the case of modern machining processes
the increase in the cutting speed need not necessarily be of major
importance, but with particular applications, such as the machining of
light metals, for instance, it may be endeavored to dispense with coolants
and lubricants or at least to reduce the use thereof and, on the other
hand, to accept a reduced cutting speed.
In the case of tools having geometrically defined cutting edges, such as,
e.g., drills, milling cutters, reamers, screw taps, core drills etc.,
preferably high-alloy tool steels, hard metals, i.e. sintered materials of
metallic hard materials such as, for instance, cermet, ceramic insert,
monocrystalline diamond, polycrystalline diamond, polycrystalline boron
nitride etc. are employed as cutting materials.
Moreover, there are known tools in which the wear resistance of the tools
is further increased by coating them with hard material layers, such as,
e.g., titanium nitride, titanium carbide and aluminium oxide.
In DE-OS 23 57 134 a cutting tool is disclosed in which a coating film of
precious metal is applied by an ion-plating method. DE-AS 12 71 495
relates to a method of manufacturing a cutting tool in which a cover layer
of copper or brass is applied to the portions not to be hardened prior to
a hardening operation.
The cutting tools known from the two a.m. publications have the common
drawback that, on the one hand, the cover layers consist of comparatively
expensive materials and the tool lives are improvable, especially when
light metals are processed.
The continuous development of the machine tools and the use of novel
methods, such as dry machining, for instance, where the workpieces are
machined without using coolants/lubricants or machining with reduced
amounts of coolant, and the endeavor to obtain more and more reduced
manufacturing tires make requirements to the tools as regards the tool
lives and the maximum obtainable cutting speeds which cannot be fully met
by conventional tools.
The object underlying the invention is to provide a cutting tool which has
a simple design and permits an improved tool life while, at the same time,
the cutting speed is increased or the amount of coolant is reduced.
This object is achieved by the features of claim 1.
The tool wear can be considerably reduced by the measure to apply a soft
slide layer containing sulphides, selenides, tellurides, such as, e.g.,
MoS.sub.2, NbS.sub.2, TaS.sub.2, WS.sub.2, MoSe.sub.2, NbSe.sub.2,
TaSe.sub.2, WSe.sub.2, MoTe.sub.2, NbTe.sub.2, WTe.sub.2 or mixed
compounds, to the cutting tool, because the chip slides off the soft slide
layer and thus the face wear is reduced and the formation of a built-up
edge is prevented. Moreover, the friction between the tool and the open
face is minimized so that the wear of the open face is reduced, too. Thus
the tool life can be considerably improved by the slide layer according to
the invention compared to conventional solutions. There are already known
some coating methods for applying wearing coats to cutting tools so that a
respective description is dispensed with. A method of the co-applicant
VILAB AG/Switzerland has turned out to be especially suited.
It is of particular advantage to apply the soft slide layer to a
wear-resisting base layer which, in turn, has been applied to the base
body of the cutting tool so that the latter is provided with two layers.
In order to ensure an optimum machining operation, the soft slide layer is
not applied in the area of the cutting edge.
It is especially advantageous when the base body of the cutting tool is
made of HSS, hard metal, cermet or ceramic material and the wear-resisting
layer consists of TiN, TiAlN, TiCN, diamond or the like.
Depending on the application, it is preferred to apply the base layer in a
thickness of 1-10 .mu., while the hardness of the base layer should be
between 2000-10000 UV and the slide layer should have a Mohs' hardness of
1-2.
The measure to form one or a plurality of grooves, especially in grooved
shape, in the flute promotes breakage of chips so that the formation of
long flowing chips, which interfere with the operating cycle, e.g. in
automatic machine tools, and impede the chip removal, is prevented. With
the short discontinuous chips a high surface quality is guaranteed, while
the chips can easily be removed. Moreover, in the case of wet machining
the groove facilitates the supply of coolants and lubricants to the
cutting portion of the tool so that the stability thereof is increased and
the carrying-off of the chip is further facilitated.
Preferably a plurality of grooves extending along the flute at parallel
distance is formed in the face.
The chip formation and the chip discharge can be further improved by
providing also the open space with groove-like recesses extending away
from the cutting edge. The supply of coolant and lubricant, too, can be
further improved by such recesses compared to the above-described
embodiment.
The chip capacity and the tool times of such a tool are superior to those
of conventional tools, even if the workpieces are machined in a dry state
or with reduced supply of coolant.
In case that the cutting edge is formed at the front of the cutting member,
such as, e.g., in drills, face mills, core drills etc., the recesses are
advantageously formed as segments of a circle or spiral on the open face
which are positioned approximately concentrically with respect to the axis
of the cutting tool.
The chip formation and the supply of coolant and lubricant can be further
improved by the fact that a recess is associated with each groove so that
the recess is practically arranged in extension of a groove.
In special cases of application it may be advantageous to form the grooves
or recesses only over a partial area of the flute and the open space,
respectively.
It has proved especially advantageous when the width and the depth of the
grooves and/or the recesses is between 0.02-2 mm, preferably 0.02-0.5 mm.
Further advantageous developments of the invention are described in the
subclaims.
In the following, preferred embodiments of the invention are explained in
detail by way of schematic drawings.
FIG. 1 is a view of the cutting member of a twist drill;
FIG. 2 is a diagrammatic top view on a bit of a drilling tool;
FIG. 3 is a three-dimensional sectional view of a cutting tool according to
the invention;
FIG. 4 is a schematic diagram for explaining the chip formation in a
cutting tool according to the invention;
FIG. 5 is a diagram comparing a conventional cutting tool with a cutting
tool according to the invention, and
FIG. 6 is a diagram comparing a conventional cutting tool with a cutting
tool provided with a slide layer.
FIG. 1 shows the cutting member 2 of a twist drill 1 which has two spiral
flutes 4, 5 extending along the cutting member 2 to the bit 6 of the
drill. Each major cutting edge 8, 9 is formed at a wedge which, on the one
hand, is formed by an open face 10 and, on the other hand, by a face 12 of
the flute 5.
Moreover, in the shown embodiment groove-like recesses 14 extending
concentrically from the major cutting edge 8 (9) to the rear edge 16 of
the open face are formed in the open face 10.
In each flute 4, 5 a plurality of adjacent grooves 18 is formed the axis of
which is disposed approximately in parallel to the axis of the flute 5
(4), i.e. the grooves 18 extend likewise spirally about the axis 20 of the
drill 1. As regards further details about the design of the grooves 18 and
the recesses 14, reference is made to FIGS. 2 and 5.
As is further indicated in FIG. 1 by dot-dash lines, the drill 1 and
especially the cutting member 2 are coated with a slide layer 20 which is
not applied, however, in the area of the major cutting edges 8, 9. The
slide layer 20 preferably comprises sulphides, solenides, tellurides, such
as, e.g., MoS.sub.2, NbS.sub.2, TaS.sub.2, WS.sub.2, MoSe.sub.2,
NbSe.sub.2, TaSe.sub.2, WSe.sub.2, MoTe.sub.2, NbTe.sub.2, WTe.sub.2 or
mixed compounds thereof. When applying such slide layer 20 the areas of
the bit 6 indicated by dot-dash lines were covered by an adequate material
so that the major cutting edges 8, 9 are constituted by a harder material.
Regarding further details about the slide layer 20, the following FIGS. 3
and 6 are referred to.
FIG. 2 shows a schematic top view on the bit 6 of the drill 1, wherein
merely the faces of the drill bit 6 are represented, whereas the minor
cutting edges of the drill rotating outside the plane of projection have
been omitted.
As one can take from this view, the two open faces 10, which are confined
in the view according to FIG. 2 an the one hand by the major cutting edges
8 and 9 and, on the other hand, by the rear edges 16, are formed by the
two flutes 4, 5. The radially outer confinement of the open faces 10 is
effected by the minor cutting edges 22 and the minor open faces 24. The
two major cutting edges 8, 9 are connected by the chisel edge 26 extending
through the axis 27 of the drill, On each open face 10 the recesses 14 are
incorporated, as mentioned already before, which are formed in the
illustrated embodiment as segments of a circle or spiral concentrical with
respect to the axis 27 of the drill 1. Each of the circular lines shown in
FIG. 2 represents the bottom of a recess 14. According to FIG. 2, moreover
the grooves 18 extending approximately perpendicularly to the plane of
projection along the flutes 4, 5 are formed in the faces of the flutes 4,
5 (perpendicular to the plane of projection). Both the grooves 18 and the
recesses 14 have an approximately undulated or U-shaped cross-section so
that the major cutting edges 8, 9 are formed in wave shape. The depth and
width of the grooves 18 and/or the recesses 14 is approx. between 0.01-2
mm, preferably 0.02-0.5 mm, depending on the individual case.
The slide layer 20 mentioned at the beginning is not formed in the area of
the major cutting edges 8, 9 so that only the areas between the dot-dash
fine in FIG. 2 and the rear edges 16 of the open faces 10 are covered with
the slide layer 20.
In special cases of application it may also be of advantage to extend the
slide layer 20 to the cutting edges 8, 9.
Due to the wave shape of the faces 12 of the flutes 4, 5 and the open faces
10, the supply of coolant/lubricant--if used--to the major cutting edges
8, 9 is considerably improved so that the wear of the drill 1 can be
substantially reduced or else the amount of coolant can be reduced.
Moreover, the undulated structure of the flute entails an earlier chip
breakage so that--as already mentioned in the beginning--comparatively
short discontinuous chips are formed which ensure a high surface quality
and, at the same time, can easily be discharged.
The superiority of this "grooved section", as it is called, vis-a-vis the
conventional ground sections is emphasized in FIG. 5. This is a comparison
of the tool life travel of two twist drills, one of which was provided
with a plane open face and a planar face or flute, while the comparison
tool was provided with the grooved section according to the invention at
the flutes 4, 5 and the open faces 10. A workpiece of 42CrMo4V was
machined by both drills, wherein the two drills were not provided with the
above-mentioned slide layer 20, Both twist drills had identical
geometrical dimensions--apart from the grooved section --and were operated
at the same cutting speed v.sub.c, the same feed f and the same cutting
depth a.sub.p.
As one can take from FIG. 5, solely by providing the grooved section the
tool life travel can be substantially improved compared to conventional
tools so that the tool lives and the maximum obtainable cutting speeds of
the tools according to the invention are superior to those of conventional
tools especially in the case of dry machining or in the case of machining
with a reduced amount of coolant/lubricant.
FIG. 3 represents a three-dimensional view of a drilling tool, wherein, for
the sake of clarity, the grooves 18 in the flutes 4, 5 are indicated as
dashed lines in the area of the major cutting edges 8, 9. The recesses 14
in the open faces 10 are indicated merely as dot-dash lines, because by
way of FIG. 3 the coating of the drill 1 is to be illustrated.
The base body of the drill may be manufactured of conventional HSS steel,
for instance, wherein either the entire drill or, as indicated in FIG. 3,
merely the cutting member 2 is provided with a hard base layer 26. This
base layer 26 may consist, e.g., of a hard ceramic material such as TiN,
TiAlN, TiCN or of diamond etc. As mentioned already at the beginning, the
PVD coating method is not discussed here, to simplify matters, but
reference is made to the relevant literature and, in particular, to the
respective patent application of VILAB.
The base layer 26 extends to the major cutting edges 8, 9, wherein in FIG.
3 the hatching indicative of the base layer 26 was not effected in the
area of the major cutting edges 8, 9.
On the base layer 26 the aforementioned slide layer 20 is formed which is
indicated by a grey shading in FIG. 3. This slide layer 20 is preferably
prepared on the basis Of sulphide, selenide or telluride and thus has
certain lubricating characteristics which will be explained in more detail
in the following. The slide layer 20 does not extend over the entire
cutting maker 2, but ends at a distance from the major cutting edges 8, 9
so that the latter are formed by the hard wear-resisting base layer 26.
I.e., the actual cutting area of the drill 1 is covered by the hard base
layer 26, which may have, for instance, a Vickers pyramid hardness of
approx. 2000-10000 HV, while the other areas of the cutting member 2,
which do not directly contribute to the machining operation, are covered
with the comparatively soft slide layer 20 which may have, for instance, a
Mohs' hardness of 1-2.
In particular cases, the slide layer 20 may also be applied directly to the
base body so that the same constitutes the base layer.
In order to illustrate the effect of this slide layer 20, FIG. 4 shows a
sectional view of a cutting edge 28 of a cutting tool during the machining
operation. A chip 32 is removed from a workpiece 30 by the feed motion in
the direction of the arrow, the cutting edge 29 being formed by the hard
and wear-resisting base layer 26 in the area where the actual machining of
the workpiece 30 is performed. The chip is removed along the face 12 and
thus moves on the slide layer 20 indicated as dashed line which supports
the gliding of the chip along the face 12 due to its sliding effect
(MoS.sub.2 . . . ). In this way, the removal of the chip from the actual
machining area is supported so that, on the one hand, the chip and thus
also thermal energy can rapidly be discharged from the workpiece and, on
the other hand, the face wear is minimized due to the special structure,
i.e. a hard base layer 26 in the cutting area and a soft slide layer 20 in
the discharging area of the flutes 4, 5, and the formation of a built-up
edge is prevented.
Moreover, by producing the slide layer 20 on the open face 10 of the tool,
the friction thereof with the machined surface 34 of the workpiece 30 is
minimized so that also the wear of the open face in the area of the
cutting edges can be reduced to a minimum. Hence by providing the slide
layer 20 the wear of the tool can be substantially reduced compared to
conventional tools having no slide layer 20.
Such tools are thus especially advantageous when used for dry machining or
for the machining with a reduced amount of coolant of light metals
(aluminium/magnesium alloys) which becomes increasingly important in the
automotive and aviation industry. When coolants and lubricants are
dispensed with or reduced, one the one hand considerable investment costs
can be saved, on the other hand the recycling or waste disposal of such
coolants/lubricants represents a problem which likewise constitutes an
increasingly important cost factor in view of strict legislative
impositions.
The superiority of coated tools to uncoated tools can be explained by way
of the comparative tests represented in FIG. 6. These tests were carried
out with a TiAlN-coated twist drill, the tests being executed on the basis
of identical machining parameters (cutting speed, feed, cutting depth).
The test series shown on the left of FIG. 6 was carried out with a
workpiece made of AlSi9, wherein an almost tripled tool life travel was
achieved by the tool provided with a hard base layer and a soft slide
layer (H+S).
The same result was obtained also with an Al alloy having a higher silicon
content (AlSil8), wherein although on the whole lower values were achieved
due to the worse machinability of this material, the coated tool, however,
exhibited a considerably longer tool life travel with otherwise equal test
conditions.
I.e. by providing the soft slide layer on a hard base layer or a hard base
body of a tool the tool life and thus also the maximum possible cutting
speeds can be substantially improved compared to conventional tools.
Optimum results can be achieved, when the tool as represented in FIGS. 1
and 3 is provided both with a grooved section and with a soft slide layer,
wherein it may be advantageous in individual cases to provide solely
either of the described improvements (grqoved section or slide layer).
When forming the grooves 18 and the recesses 14, radii (depths and widths)
ranging from 0.01-2 mm, preferably 0.02-0.5 mm, are preferred. Such
grooves 18 and recesses 14 can be produced during grinding the flutes an
the drill bit, resp., in one working cycle so that no separate grinding
operations and tools are necessary for providing the grooves/recesses.
The slide layer 20 can be prepared by ion sputtering so that this layer is
not only applied to the surface of the base layer 26 but also partly
diffuses into the base layer.
The invention is not restricted to the use with drilling tools, of course,
but the grooved section according to the invention and/or the slide layer
according to the invention are also applicable to other cutting tools,
preferably to those having a geometrically defined cutting face.
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